Hydraulic cylinder unit



' July 19, 1960 s HYDRAULIC CYLINDER UNIT Filed Aug. 21,- 1957 3 Sheets-Sheet 2 .Z'nverzi-w Maul-us GZaa' i 4 ml ,fmwflw;

July 19, 1960 v M. GLAS 'HYDRAULIC CYLINDER UNIT 1 5 Sheets-Sheet 3 Filed Aug. 21, 1957 I-n vevzfm Maulus 6 2:5

, rates HYDRAULIC CYLDIDER UNIT Maurus Glas, Jordenstrasse, 10, Frankfurt am Main,

' Germany The present invention relates to a hydraulic power unit with a double piston in which the larger piston is slidable in a main cylinder and the smaller piston in a rapid-feed cylinder, and in which these cylinder are separated by a partition and are provided with connections for supplying a pressure medium so as to act upon one or the other side of the pistons.

It is one of the objects of the present invention to provide a hydraulic power unit of the above-mentioned type which is of a very compact design and permits a considerable saving in the amount of hydraulic pressure medium required for its operation.

This object of the invention is attained primarily by the provision of a double piston with a continuous piston rod and the provision of a pressure-transmitting piston which passes through the partition into the main cylinder, may be hydraulically. acted upon from both sides, and is slidable within a part of the main cylinder which annularly surrounds the rapid-feed cylinder. This inventive design results in a considerable saving in the volume of pressure medium required for producing the rapid-feed or forward stroke.

More specifically, for this purpose as well as for reducing the volume of pressure medium required for carrying out the return stroke, the hydraulic power unit according to the invention is designed as follows:

One end of the rapid-feed cylinder partly extends into one end of the main cylinder which is closed at its other end. The end of the rapid-feed cylinder which extends into the main cylinder is closed by a cylinder cover which forms a part of the partition which separates the main cylinder from the rapid-feed cylinder. Thus, a part of the rapid-feed cylinder and the part of the main cylinder which surrounds the rapid-feed cylinder in a spaced relation thereto together form an annular chamber which constitutes a part of the cylinder chamber of the main cylinder which is acted upon by the pressure medium during the forward stroke. The other part of the partition separating the main'cylinder from the rapid-feed cylinder is formed by an inner flange provided on one end of the main cylinder and by an outer flange on the rapid-feed cylinder opposite to the first flange. The annular chamber formed by these two flanges serves as the inlet opening for the tubular part of the pressure-transmitting piston which is designed in the shape of a tubular plunger piston. This tubular part surrounds the rapid feed cylinder at such a spaced relation thereto that an annular cylinder chamber is formed in which the pressure-transmitting piston is slidable. At one end opposite to the mentioned flanges, this piston carries an inner flange which closes off the annular cylinder chamber, as well as an outer flange. This latter flange is slidable within an extension of the jacket of the main cylinder which surrounds the pressure-transmitting piston at a spaced relation thereto and is closed at its outer end. The further annular chamber thus formed constitutes the 2,945,353 Patented July 19, 1960 ice second cylinder chamber for the pressure-transmitting design which, in turn, permits the application of a double" piston with a continuous piston rod, it is possible according to the invention to separate the rapid-feed cylinder completely from the main cylinder and to omit a valve for connecting these two cylinders. The use of a continuous piston rod furthermore permits the delivery of compressive or traction forces of equal size by the piston' rod and at an equal efliciency. V

The main cylinder according to the invention may be formed by a cylindrical sleeve which is exchangeable and mounted within an outer jacket which also surrounds the rapid-feed cylinder as well as the pressure-transmitting piston, and is provided along its outer surface with longitudinally extending grooves, the ends of which communicate with the inside of the cylindrical sleeve.

The main cylinder may, however, also be made of a single piece of material. In this case, the jacket of this cylinder is provided with longitudinally extending bores and radial bores which communicate with the longitudinal bores and lead into the cylinder chambers of the main cylinder so that the two cylinder chambers which are separated by the main piston are thus connected with each other.

The cylinder chambers of the main cylinder and the rapid-feed cylinder which are acted upon by the hydraulic medium during the return stroke of the piston are further connected with each other by a bore extending in the axial direction within the piston rod and by radial bores communicating therewith.

The double piston including the piston rod also may have a bore extending therethrough in the axial direction. In this case it will be necessary to arrange the other axial bore, through which the cylinder chambers communicate with each other during the return stroke of the piston, within the wall of the piston rod.

The rapid-feed cylinder which is provided with the bores which are required for elfecting the forward and return stroke of the small piston and the pressure-transmitting piston is supported at one end by an extension of the outer cylinder jacket which is provided with the main inlet and outlet connections for the hydraulic pressure medium which communicate with the bores in the rapidfeed cylinder. 7

The extension of the outer jacket may be formed by a socketlike sleeve which is screwed thereon and has inner screw threads within its free end, into which a pluglike stop member is screwed which is associated with another stop member which is mounted on the piston rod and may beadjustable by being screwed thereon. It is thus possible tore'gulate the extent of the piston stroke and to influence the size of the eflective volume of the pressure medium.

Accordingto a modification of the invention, the pressure-exerting end of the piston rod may be surrounded by a pressure sleeve which advances during the forward strokeand precedes the same. In this case, thelarge main piston is made in the form of a cylinder, and this pressure sleeve is driven by a special piston which is slidable within the large cylinder-like piston and, acts upon the pressure sleeve by means of pins which are slidable within one end wall of the large piston. This a a piston which acts upon the pressure sleeve is, in turn, acted upon by the pressure medium which is displaced during the forward stroke of the small piston. The cylinder-chamber of the pressure sleeve piston communicates with the cylinder chamber of the main cylinder which is.

not underhydraulic pressure during its forward stroke so that the movement of the largepiston and thus also the piston rod is at such time retarded relative to the forward stroke of the pressure sleeve.

In order to insure that the pressure medium which is displaced from the two cylinder chambers of the main. cylinder will have the same volume during the forward and return strokes, that portion of the piston rod, which is adjacent to the large piston and passes into the cylinder chamber ofthe main cylinder which is acted upon by the pressure medium during the forward stroke, is made of the same diameter as the pressure sleeve.

Further objects, features, and advantages of the present invention will be apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which- Fig. 1 shows across section of the hydraulic cylinder unit according to the invention, taken along the longitudinal axis thereof and illustrating the piston in its starting position;

Fig. 2 shows a portion of Fig. 1 on an enlarged scale;

Fig. .3 shows a view similar to Fig. l but illustrating the pistons in a position after the rapid-forward stroke and during the actual compression stroke;

' Fig. 4 shows a side view of piston rod with an axial bore extending therethrough;

Fig. 5 shows a modified portion of Fig. 1 with amain cylinder of a slightly different design; while Fig. 6 shows a modified portion of Fig. l and illustrates the hydraulic cylinder unit with an additional pressure sleeve.

Referring to the drawings, and first particularly to Figs. 1 to 3, the hydraulic cylinder unit according to the invention comprises a double piston with a continuous piston rod. The larger main piston is designated by 36, the smaller rapid-feed piston by 19, and the piston rod by 4. For simplifying the manufacture, the larger piston 36 is made of two parts 36' and 36" which are connected to each other by bolts 39. This also requires a division of piston rod 4 into parts 4 and 4", the ends of which facing toward each othercarry parts 36' and 36", respectively, of piston 36.

The smaller piston 1 runs within a rapid-feed cylinder 22, whereas the larger piston 36 runs in a main or work cylinder 26, one end of which is closed by a screw plug 28 forming a cylinder cover. One end of the rapid-feed cylinder 22 is closed by a cover 22' through which piston rod 4 extends and which forms a part of the wall separating the main cylinder 26 from the rapid-free cylinder 22. This closed end of cylinder 22 extends into main cylinder 26 and thereby forms an annular chamber 7. The other end of rapid-feed cylinder 22, which is closed by a cover 22" through which piston rod 4 likewise extends, is disposed within a cylindrical extension of main cylinder 26 which forms a sleeve 23 which extends coaxially to main cylinder 26 and is connected thereto by means ofv screw threads 24. t

Within its outer open end, sleeve 23 is provided with internal screw threads 24 into which a setting ring 25 1s screwed which may serve as a stop member for limiting the extent ofthe return stroke of 'piston rod 4. For this purpose, piston rod 4 also. carries a pluglike setting ring 21 which is adapted to engage with stop-ring 25 and which may also serve for limiting the forward stroke of piston rod 4. For the latter purpose, setting ring 21 is provided with internal screw threads 24) and thus adjustably mounted on corresponding outer screw threads on piston rod 4. The forward stroke of piston rod 4 is thus limited by the engagement of the inner end surface of setting ring 21 against the inner shoulder of extension-sleeve 23;

Main cylinder 26 consists of an inner cylindrical sleeve 26' which has outer longitudinal grooves 6 and is disposed Within an outer jacket 26". The end of sleeve 26' facing toward screw plug 28 is provided with segmental recesses it) which communicate with longitudinal grooves 6. Near its other end, sleeve 26 is provided with radially extending b ores lti which communicate with a longitudinal grooves 6. A spring ring 40, which is sprung into an annular groove in jacket 26" prevents the inner cylindrical sleeve 26 from shifting in one axial direction.

The design and construction of main cylinder 26, as above described permits jacket 26" to be exchangeable as well as reversible so that the outer sleeve 23 and screw plug 28 may be screwed into either end of jacket 26".

The modification of theinven tion as illustrated in Fig. 5 shows that main cylinder 26a may also consist of a single part. In this case, the cylinder jacket is provided with several longitud nal bores 6a, the ends of which communicate with the inside So and 7a of. the'cylinder through radial bores 116a.

Referring again to Figs. 1 to 3, the fiangelike head 28 of the pressure-transmitting piston 18 is slidable Within a diametrically enlarged portion of main cylinder 26, that is, directly along the inner wall of the outer jacket 26". The other end of piston 18 is slidable between an inner flange'iA on main cylinder 26 and an opposite outer flange 15 on rapid-feed cylinder 22. These two flanges together form a further part of the intermediate wall separating main cylinder 26 from the rapid-feed cylinder 22. The tubular portion 18" of the pressure-transmitting piston 18 surrounds cylinder 22, leaving a small intermediate annular clearance 17 forming a pressure-transmitting cylinder chamber. This cylinder chamber 17 is closed at both ends by the outer flange 15 of the rapidfeed cylinder and an inner flange 16 on head 18' of the pressure-transmitting piston 18. The annular'space between jacket 26" andthe tubular portion 18 of piston 18 which is not filled with pressure medium communicates through at least one opening 41 with the outer atmosphere.

As illustrated on an enlarged scale in Fig. 2, rapidfeed cylinder 22 1s provided at the side facing toward the inlet 1 of the pressure medium with a longitudinal bore 2 which is closed toward the outside by means of a plug 44 or the like and communicates through an opening 42 with inlet 1 and through an opening 43 with cylinder chamber 12' of the rapid-feed cylinder 22 which is located behind the smaller piston 19.

On the outer end of piston head 18' of the pressuretransmitting piston 18, this head is provided at the point where it engages with the rapid-feed cylinder 22 wih an annular recess 3 which communicates with the longitudinal bore 2 in cylinder 22 through a small opening 8,

bore 2 communicates with a cylinder chamber 17 which is formed during the advance ofthe pressme-transmitting piston 18 between piston'head 18 and sleeve 23 which serves as a cylinder cover.

At its opposite side Where an outlet 13'for the pressure medium is provided in sleeve 23, rapid-feed cylinder 22 has a second longitudinal bore d5 which is closed by a plug 46. This bore45 communicates through an opening 47 with outlet 13. Cylinder chamber 12 of rapidfeed cylinder 22 which is disposed infront of the small piston 19, as seen in the direction of the forward stroke, communicates through an opening $8 with the longitudinal bore 45 which, in turn, communicates through an opening 439 with chamher 17 of the pressure-transmititng cylinder.

The outer connections 1 audit?) for the pressure medium may beexactly or almost exactly apposite to each other so that almost the entirelength of the outer jacket interfering with any tools or other elements upon which a compressive or pulling force is to be exerted.

The flow of pressure medium into cylinder chamber 17' of the pressure-transmitting piston, which is controlled in the embodiment as illustrated in Figs. 1 to 3 by the openings 8 and 9, may be further controlled by an adjustable valve, not shown, which may be mounted at a suitable point.

The operation of the hydraulic cylinder unit as'illustrated in Figs. 1 to 3 is as follows:

When piston rod 4 carries out its forward stroke, that is, in the downward direction, as shown in the drawing, the pressure medium coming from a pressure generator, not shown, enters through inlet 1 in sleeve 23 and passes through opening 42 into the longitudinal bore 2 of rapidfeed cylinder 22 and then through opening 43 into cylinder chamber 12' of cylinder 22, that is, at a point behind the small piston 19. This produces the rapid-feed stroke of the double piston 19, 36. Such rapid-feed stroke by means of the small piston surface of piston 19 is possible because the pressure medium contained in cylinder chamber 5 of the main cylinder 26 is able to pass through the segmental recesses longitudinal grooves 6, and radial bores 10 into cylinder chamber 7 of main cylinder 26 which is disposed behind the large piston 36. The pressure medium contained in cylinder chamber 12 of rapid-feed cylinder 22 in front of the small piston 19 may'flow oflf through opening 48, bore 45, opening 47 and outlet 13.

As soon as a pressure ram or the like which is connected to the lower end 4" of piston rod 4 hits upon a workpiece and the movement of pistons 19 and 36 is thereby stopped, the pressure medium will flow from longitudinal bore 2 of rapid-feed cylinder 22 through the small opening 8 into the annular recess 3 of head 18 of piston 18 and moves the latter in the forward or feeding direction. During this forward movement, piston head 18 frees the larger opening 9 which connects the longitudinal bore 2 of rapid-feed cylinder 22 with the cylinder chamber 17' which has then been formed behind the pressure-transmitting piston 18. Consequently, piston head 18' will now be acted upon by the entire flow of the pressure medium. During the forward movement of piston 18, radial bores 10 of the main cylinder 26 will be closed, the tubular portion 18" of piston 18 penetrates into cylinder chamber 7 of the main cylinder behind piston 36, and initiates the force transmission, as illustrated in Fig. 3. The pressure medium contained in cylinder chamber 5 of main cylinder 26, which can now no longer pass outwardly through the segmental recesses 10, flows through radial bores 11 and longitudinal bore 11 in piston rod 4 and piston 36 into cylinder chamber 12 of rapid-feed cylinder 22 and thence through opening 48,1ongitudinal bore 45 in rapid-feed cylinder 22 and opening 47 into outlet 13. The pressure medium contained in cylinder chamber 17 will then be discharged through opening 49.

The actual compression operation is carried out during this forward stroke of the pressure-transmitting piston 18 and piston rod '4 with pistons 36 and 19'.

As soon as piston rod 4 with pistons 36 and 19 has arrived at the end of the power stroke, which is limited, for example, by the engagement of the end surface of setting ring 21 against the inner end surface or bottom 27 of sleeve 23, the flow of the pressure medium is reversed so that the former inlet 1 will now become the outlet and the former outlet 13 will now become the inlet.

The pressure medium will then pass from inlet 13 through opening '47 into longitudinal bore 45 of rapidfeed cylinder 22 from where it will flow through opening 48 into cylinder chamber 12 of rapid-feed cylinder 22 and through opening 49 into cylinder chamber 17. The pressure-transmitting piston 18 will then at first be forced backwardly, that is, upwardly, as shown in the drawing,

while the double piston 36, 19 will'at first inoiie back wardly only to the extent of the volume cleared by piston 18 in cylinder chamber 7 of main cylinder 26. As soon as the tubular part 18" of pressure-transmitting piston 18 has freed the radial bores 10' of main cylinder 26, the rapid return stroke starts since the pressure medium contained in cylinder chamber 7 of main cylinder 26 can pass through radial bores 10, longitudinal grooves 6, and segmental recesses 10' into cylinder chamber 5 of the main cylinder. Otherwise, the pressuremedium flows during the return stroke along the following path: The pressure medium contained in the pressure-transmitting cylinder chamber 17 flows through the large opening 9 and the small opening 8 into longitudinal bore 2 of rapid-feed cylinder 22 and then through opening 42 into connecting socket 1 which now forms the outlet. The pressure medium contained in cylinder chamber 12 of rapid-feed cylinder 22 behind the small piston 19 flows off through openings 43 and 42. Insofar as cylinder chamber. 5 of main cylinder'26 is not being filled with the pressure medium contained in cylinder chamber 7, such medium will be supplied to chamber 5 from cylinder chamber 12 of rapid-feed cylinder 22 through radial bores 11 and longitudinal bore 11 in piston rod 4. The small piston 19 is also acted upon by the pressure medium in cylinder chamber 12. In the event that the return stroke might require a greater amount of energy than can be produced by the small surface of piston 19 as long as radial bores 10 are not as yet freed by piston 18, such energy will be supplied by the hydraulic pressure upon the large piston 36 in cylinder chamber 5.

The lower end 50 of piston rod 4 may be connected to tools or other elements which are to operate under pressure, while the other end 51 of piston rod 4 may be connected to such tools or other elements which are to carry out a pulling action. However, if desired, both ends 50 and 51 of piston rod 4 may also be connected to such tools or elements.

Inlthe modification of the double piston 19a and 36a, as illustrated in Fig. 4, in which the individual parts are connected to each other by piston rod 4a, this piston rod is provided with a bore 31 extending axially therethrough. In this case, bore 34a, which corresponds to bore 11 in Figs. 1' and 3 and connects cylinder chamber 5 and 12 which are under pressure during the return stroke of the piston, is disposed oif-center within the wall of piston rod 4a and communicates with the cylinder chamber 5 and 12 through radial bores 34a and 34a".

The modification of the inventive hydraulic power unit as illustrated in Fig. 6 differs from the embodiment as shown in Figs. '1 to 3 by the fact that the lower part 4" of the piston rod is enclosed by a pressure sleeve 32 which is slidably guided by the inner wall of the pluglike cylinder cover 28. If, for example, the lower part 4" of the piston rod is connected to a riveting set, this pressure sleeve 32 may be used for pressing the parts which are to be riveted together against a dolly or the like so that these parts will thus be firmly pressed together before the actual riveting operation starts.

' For operating the pressure sleeve 32, the large piston 36b is designed in the form of a closed cylinder. For this purpose, its two parts 36b and 36b" areconnected to each other by a cylindrical sleeve 33 which together with head portion 36b may, for example, consist of a single piece and be connected to part 36b" by screw threads 34. Piston 3611 thus forms a cylinder in which a piston 29 can slide so as to act during the forward stroke upon pins 30 which are slidable within bores 35 in piston part 3612 and, in turn, act upon the end surface of a flang 37 on pressure sleeve 32. r

I When piston 29 which is adapted to act upon pressure sleeve 32 is in its basic position, cylinder chamber 55 of piston 36b is formed by a recess 52 behind piston 29and :by a central recess 52 which communicate with longitudinal bore 11 in piston rod 4 and are thus supplied with pressure mediums.

' Parts 365 and 33 of piston 36b have a slightly smaller diameter than the head portion 36b so that an annular clearance 54 is formed between these smaller parts and the inner wall of main cylinder 26, which communicates with cylinder chamber 52through radial bores 38. Cylinder chamber 53 of piston 3621 which is not acted upon by the pressure medium is maintained under atmospheric pressure by communicating with the outer atmosphere through an axial bore 31 in the lower part 4" of the piston rod. t

In order to insure that the same volume of pressure medium will be displaced in cylinder chambers 5 and 7 of main cylinder 26 during the forward and return strokes of piston rod 4, the upper part 4b of piston rod 4 which penetrates intocylinder chamber '7 of main cylinder 26 is made of the same diameter as pressure sleeve 32.

Insofar as the hydraulic power unit as illustrated in Fig. 6 differs from the embodiment shown in Figs. 1 to 3, its operation is as follows:

The pressure medium enters through inlet 1 and passes through openings 42 and 43 into cylinder chamber 12' of rapid-feed cylinder 22 where it presses the small piston 19 forwardly. The pressure medium thus displaced in cylinder chamber 12 may then act through radial bore ill, as shown in Fig. 1, and axial bore 11 of the upper part 4 of the piston rod, as shown in Fig. 6, upon piston 29 which is thereby moved downwardly. The pressure medium which thus passes into cylinder chamber 55 of piston 36b may flow through radial bores 38 and the annular clearance 54 into cylinder chamber 5 of main cylinder 26 and thus acts upon piston 36b in a direction opposite to the forward stroke thereof so that the movement of piston 36b will be retarded and pressure sleeve 32 will be pushed forwardly relative to the lower part 4-" of the piston rod. Pressure sleeve 32 then acts upon the workpieces to be riveted so as to press them together before the actual compression stroke occurs with the assistance of the pressure-transmitting piston 18. Otherwise the operation is the same as described with reference to Figs. 1 to 3.

The return stroke of pistons 19, 36b, and 18 also proceeds in the same manner as described with reference to Figs. 1 to 3. However, the pressuremedium then acts through longitudinal bore 11 upon piston 29 in the forward direction of pressure sleeve 32, so that the respective tool which is connected to the lower part 4" of the piston rod will separate sooner from the work-piece than pressure sleeve 32. If, for example, stamping operations arebeing carried out, this will prevent the stamped parts from adhering to the tool since they will be stripped off from the tool by pressure sleeve 32.

'If desired, one or more of the hydraulic power units as described and illustrated may also be installed in hydraulic presses or the like and in a manner so as to be easily exchangeable.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments but is capable of numerous modifications within the scope of the appended claims.

- Having thus fully disclosed 1. A hydraulic cylinder unit comprising an external cylinder having a part ofgreater inner diameter and a main cylinder part of less inner diameter, a rapid feed cylinder of less outer diameter than said inner diameter of said external cylinder and being concentrically arranged withinsaidtexternallcylinder part of greater inner diameter and partly penetrating into said main cylinder, part thereby forming a first annular cylinder chamber between said external cylinder part of greater inner diameter and my invention, what I claim said rapid feed cylinder, and a, second annular cylinder chamber between a portion of said main cylinder part and said rapid feed cylinder, a partition at the end of said main cylinder part surrounding said rapid feed cylinder, said partition having an annular opening connecting said main cylinder part and said first annular cylinder chamber, a double piston having a larger piston slidable in said main cylinder part and a smaller piston slidable in said rapid feed cylinder, a piston rod connecting both pistons and penetrating one front wall of said rapid feed cylinder and having an extension part penetrating one front wall of said main cylinder part for work performance externally of said main cylinder part, a pressure transmitting piston having an annular head slidable in said first annular cylinder chamber on said rapid feed cylinder, and an integral tubular portion of less outer diameter than said annular head and surrounding said rapid feed cylinder in spaced relation thereto, said tubular portion projecting into said annular opening and being adapted when sliding to enter said second annular cylinder chamber, and said external cylinder and said rapid feed cylinder being provided with connections for supplying a pressure medium for acting selectively upon either side of said pistons.

2. A hydraulic cylinder unit according to claim 1 in which'the external cylinder includes a cylindrical sleeve forming said main cylinder part and being exchangeably disposed within said external cylinder, the outer diameter of said sleeve corresponding to the inner diameter'of said external cylinder, said sleeve being provided along its outer surface with longitudinally extending grooves which communicate with the inside of said sleeve near one end of the cylindrical sleeve and at the opposite end surface of the cylindrical sleeve abut against the front wall of said external cylinder through annular segmental recesses.

3. A hydraulic cylinder unit according to claim 1 in which said connections for supplying a pressure medium for acting selectively upon either side of the pistons include in said external cylinder longitudinally extending bores and radial bores associated with said longitudinal bores for interconnecting the cylinder chambers of the main cylinder part, the piston rod having a bore therein extending inv a longitudinal direction and radial bores associated therewith at the ends thereof for interconnecting the cylinder chambers of the main cylinder part and of the rapid feed cylinder, respectively, which are acted upon by the pressure medium during the return stroke of the double piston, in the rapid feed cylinder, a bore therein extending in longitudinal direction and radial bores associated therewith for interconnecting the pressure medium supply with the cylinder chambers of the rapid feed cylinder and the first annular cylinder chamber, respectively, which are acted upon by the pressure medium during the forward stroke of the double piston and of the pressure transmitting piston, and said rapid feed cylinder having a second bore therein extending in longitudinal direction and radial bores associated therewith for interconnecting the pressure medium supply with the cylinder chambers of the rapid feed cylinder and of the first annular cylinder chamber, respectively, which are acted upon by the pressure medium during the return stroke of the double piston and of the pressure transmitting piston.

4-. A hydraulic cylinder unit according to claim 1 in which the external cylinder includes one front wall which is provided at one end of the rapid feed cylinder with a radial main connection for supplying the pressure medium which communicates with the bores of' the rapid feed 7 cylinder.

9 by screw threads, and said first plug serving as a stop member for said second plug.

6. A hydraulic cylinder unit according to claim 1, including a pressure sleeve surrounding said extension part of said piston rod for work penformance externally of said main cylinder part and being adapted to precede the pressure-exerting end of said piston rod during the forward stroke, an external piston slidable within an inner cylinder chamber provided within said larger piston, pins slidably guided within a front wall of said larger piston and being adapted to transmit the forward stroke motion of said internal piston to one end of said pressure sleeve, an axially extending bore provided in the piston rod, one end of said axial bore communicating with one inner cylinder chamber portion of said larger piston the other end of the axial bore communicating through a radial bore with said chamber of the rapid feed cylinder which is acted upon by the pressure medium during the return stroke of the double piston, the part of the larger piston surrounding said one inner cylinder portion having a smaller outer diameter than the body of the larger piston for forming an annular cylinder chamber part between the smaller outer diameter part of the larger piston and the external cylinder, said annular cylinder chamber part being, by radial bores provided in the larger piston in communication with said one inner cylinder chamber portion, the other inner cylinder chamber being in communication with the open air by an axial bore of the extension part of the piston rod.

7. A hydraulic cylinder unit according to claim 6, in which the inner diameter of the end of the rapid feed cylinder penetrating into said main cylinder part and the outer diameter of the part of the piston rod adjacent to the larger piston are, at least over a length corresponding to a stroke length, the same as the outer diameter of the pressure sleeve.

8. A hydraulic cylinder unit according to claim 1, in which an axial bore in the piston rod extends from one end to the other end thereof, and .a second bore extend- ,ing in longitudinal direction parallel to said axial bore,

and radial bores associated with said second bore at the ends thereof for interconnecting the cylinder chambers ,of the main cylinder part and of the rapid feed cylinder respectively, which are acted upon by the pressure medium during the return stroke of the double piston.

References Cited in the file of this patent UNITED STATES PATENTS 2,665,554 Rockwell Jan. 12, 1954 

